1. Field of the Invention
In general, the invention relates to the field of wheeled transportation. More particularly, the invention relates to lightweight, low-cost wheeled vehicles.
2. State of the Art
The population continues to increase, and at the same time, there is a continuing shift of population from small towns to major urban centers, exacerbating the highway congestion and urban sprawl that have characterized many large American cities since the mid-twentieth century. There is a growing belief that the favored mode of transportation, individually owned automobiles, imposes unacceptable environmental burdens and adversely affects quality of life. As a result of these forces, effective modes of urban mass transit have acquired a new priority. A sure sign of the new emphasis on providing effective vehicles and systems for urban mass transit is the rapidly increasing demand for urban transit buses. In just the United States, the current capital stock comprises at least fifty-five thousand separate vehicles; and the dollar value of annual purchases of new buses is well in excess of one billion dollars. The number of new units purchased is increasing at a rate of approximately ten to fifteen percent per year. While much of the increased demand has come from the public sector, the demand for efficient, cost-effective buses is increasing in private sector activities as well; for example, point-to-point shuttling, tourism, education, inter-city transit and recreation.
Along with the increased demand for buses, there are also emerging increased expectations, especially from public sector purchasers and regulators, of the vehicles themselves, leading to a demand for bus designs that reduce public sector costs related to roadway maintenance and repair, street and highway expansion and parking; while also ameliorating social costs related to noise pollution, air pollution, long commute times, while providing increased handicapped accessibility.
Even in the face of substantial government subsidies for development of new bus technologies, significant changes to conventional bus technology have been slow in coming. By and large, efforts to integrate new materials and power alternatives have been insufficient to address changing expectations of urban transportation managers and passengers, or to significantly reduce operating costs and initial purchase costs. However, dwindling petroleum reserves and an increasing concern about the greenhouse effect are creating a new sense of urgency. The prior art reveals many attempts to improve manufacturability of buses, decrease curb weight, increase maneuverability and safety, increase passenger comfort, and improve fuel efficiency.
Thus, several urban transit vehicles that employ modular construction techniques are described. For example, V. Belik, B. Kurach, Y. Trach, Module element of city bus or like vehicle and bus assembled on the basis of such module elements, U.S. Pat. No. 4,469,369 (Sep. 4, 1984) describe a module element for a city bus that is itself fabricated from a chassis unit, a door section, and a window section. The modules may be left-handed or right-handed. Different versions of the chassis unit are provided according to whether it is to function as a drive unit or a steering unit. Modules are assembled with front and rear elements and varying numbers of center sections to provide buses of varying size and capacity.
H. Förster, Universal vehicle system for the public local traffic, U.S. Pat. No. 4,596,192 (Jun. 24, 1986) describes a vehicle system for local public passenger transportation in which differing vehicle components are assembled to create vehicles of different size and capacity. Vehicles usable only on tracks, ones for use with or without tracks and ones for use only without tracks are possible.
L. Bergström, H. Eklund, J. Pettersson, Chassis for a bus, PCT Application No. SE94/01108 (Nov. 24, 1993) describe a bus chassis in which different versions of a front-end module are readily created by combining different front wheel modules and driver's compartment modules so that the height of the driver's compartment in relation to the rest of the bus varies.
However, none of the examples above contemplate the use of unconventional suspension systems to enhance ride quality and reduce load requirements, permitting the use of composite building materials and lightweight parts. Nor do they consider improving vehicle mobility and maneuverability through the provision of features such as all-wheel drive and all wheel-steering, or alternate power strategies such as hybrid power systems, or microprocessor control of the various vehicle subsystems.
D. Quattrini, A. Carlo, Electrically powered urban public transport vehicle with a floor at a reduced height, European Patent Application No. 90202043 (Aug. 11, 1989) describes an urban mass transit vehicle having a passenger compartment at a reduced height above the ground, with the wheels being located near the front and end regions. Each axle is provided with its own drive motor, providing all-wheel drive, allowing for optimal traction under adverse weather and road conditions. Additionally, all wheel steering is included to enhance maneuverability in confined spaces. Quadratttini, et al., don't however envisage the use of hybrid power systems, or unconventional suspensions that allow reduction of load requirements, permitting construction of a vehicle with composite materials, and lightweight off-the shelf parts. Moreover, they do not think of cellular body construction.
Municipality of Rotterdam, Manufacturing and implementation of a lightweight hybrid bus, www.eltis.org/data/101e.htm, describes a bus incorporating a modular light body system that allows identical building systems for different sized vehicles, a substantial weight reduction, and hybrid traction. There is no mention of what features in the construction are responsible for the weight reduction, nor are features such as all-wheel drive, all-wheel steering, improved suspension systems, or microprocessor control of vehicle subsystems considered.
L. Woods, J. Hamilton, Computer optimized adaptive suspension system having combined shock absorber/air spring unit, U.S. Pat. No. 4,468,739 (Aug. 28, 1984) and L. Woods, J. Hamilton, Computer optimized adaptive suspension system, U.S. Pat. No. 4,634,142 (Jan. 6, 1987) describe a vehicle suspension system in which a computer controls damping and spring forces to optimize ride and handling characteristics under a wide range of driving conditions. While a variety of suspension characteristics are achievable by programming the controller, there is no evidence that the suspension system described incorporates features that reduce load bearing requirements for the vehicle frame, allowing the vehicle to be manufactured from lightweight, off-the-shelf automobile or light truck parts. Furthermore, the described suspension provides no means of adjusting vehicle height relative to the roadway. And there is no suggestion that the suspension is appropriate for use in urban mass transit vehicles.
P. Eisen, All-wheel steering for motor vehicles, U.S. Pat. No. 5,137,292 (Aug. 11, 1992) describes an all-wheel steering arrangement having a coupler mechanism between the front and rear axles. There is no indication that the described arrangement is suitable for anything other than vehicles having two axles. What's more, the steering system is a simple, mechanical system. There is no provision for individual control of each axle a microprocessor or controller in a multi-axle vehicle.
There exists, therefore a need for an urban transit vehicle that:                is affordable and easily manufactured;        is lightweight;        is highly maneuverable;        provides exceptional passenger comfort;        is energy-efficient; and        minimizes or eliminates air and noise pollution commonly associated with buses.        
It would be a significant technological advance to provide a cellular body construction, in which vehicles are constructed from identical components or cells, one cell including a passenger compartment, the associated floor, sidewalls, roof, an axle with drive train, wheels, suspension, steering and brakes. It would be advantageous to construct vehicles of varying size, simply by “bolting together” the required number of cells, easily allowing the manufacture of vehicles having any number of evenly spaced axles. It would be desirable to provide a suspension system in which each wheel has its own independent suspension, thereby providing greatly improved ride quality. It would be an advantage to configure the suspension system to permit reduced load carrying requirements on the vehicle frame, allowing the vehicle to be fabricated from lightweight, off-the-shelf parts and lightweight materials. It would be a great benefit to equip the vehicle with an energy-efficient, hybrid fuel system, so that reliance on increasingly scarce and environmentally unfriendly fossil fuels is greatly reduced or eliminated. It would also be desirable to equip the vehicle with all-wheel steering, thus permitting a much-reduced steering radius and allowing the vehicle to be easily maneuvered in city traffic as well as on narrow, residential streets. It would be advantageous to provide an advanced control system that integrated control of the steering, suspension, braking and power systems.